In many cases the useful life of vegetable cooking oil commonly used in commercial deep fat fryers or the like can be extended by removing sedimentary solids from the oil. Many components, e.g., salt or eggs, of product coatings, whether batter or breading, can cause oil problems including an acceleration or build-up of free fatty acid in the oil. In addition, charred particles of sedimentary solids may transfer a char taste to the oil, and very fine charred particles may also give a premature charred color to the oil. The solution to these problems is to remove the sedimentary solids, whether crumbs or finely divided suspended particles, from the oil before these problems occur.
Another area of concern is the fact that crumb accumulation, wherein heavier particles settle out of the oil, can adversely affect the performance of the fryer, whether it is a direct heated type or an indirect heated type of fryer as those fryer structures are referred to in the related art. With either heating method, crumb accumulation can adversely affect heat transfer. Removal of the sedimentary solids from the cooking oil will prevent such problems from arising.
The assignee's filter apparatus as disclosed in its U.S. Pat. No. 4,081,375 utilizes a single stage filtering structure incorporating a reservoir into which particle contaminated cooking oil from the fryer unit is disposed. The bottom portion of the reservoir defines an open-end compartment under negative pressure which is effective to draw treated oil out of the compartment to be returned to the fryer. An endless metallic mesh filter belt is disposed over the open end of the compartment in the path of oil movement in the reservoir under the influence of the negative pressure source and is operable to entrap solid particles thereon. Such entrapment continues until a layer of particles is formed on the portion of said belt overlying the compartment at which time the belt is actuated to place another "clean" portion of the belt over said compartment opening. Alternatively, the endless belt may be continuously actuated at a relatively slow rate over said compartment. The layer of particles entrapped on the belt may then be removed by any suitable means such as a blade extending transversely across the belt adjacent its one end and said particle layer is then discarded.
A primary advantage of the two-stage filter apparatus of the present invention is that the removal of substantially all of the particulate materials may be accomplished serially in such manner as to provide substantially particulate-free oil to be returned to the fryer than heretofore capable.
A further advantage of the filter apparatus of the present invention is that it incorporates two stages of filtration, one defined as a coarse filter stage wherein relatively large particles as for example 5/32" in diameter may be removed from the oil and the second as a fine filter stage wherein particles as small as 20 microns may be removed from the oil.
Another advantage represented by the two-stage filter of the present invention is that the two stages are serially connected whereby oil containing particulate material is initially presented to the coarse filter stage and then to the fine filter stage, and further wherein filtered oil from the fine filter stage is re-connected or re-cycled into the input of the coarse filter stage and thereby re-cycled through both coarse and fine filter stages to provide an output of substantially particulate-free oil for return to the fryer.
Other advantages of the present invention will become apparent from the following description of a preferred embodiment thereof and as is also set forth in the accompanying drawings.